1. Field of the Invention
The present invention relates to a resin-packaged LED light source for use in a photointerrupter, for example.
2. Description of the Related Art
FIG. 3 illustrates an example of prior art LED light source. The illustrated LED light source 101 is made as a light emitting unit of a photointerrupter. The light source 101 includes a rectangular LED chip 102 and a resin package 3 enclosing the chip.
The LED chip 102 has a chip body 21 including a light emitting layer 21c. The chip body 21 has a lower surface formed with a lower electrode 22 and an upper surface formed with an upper electrode 23. When a predetermined voltage is applied across the lower electrode 22 and the upper electrode 23, light is emitted from the light emitting layer 21c. More specifically, light is emitted radially from a certain point of the light emitting layer 21c. 
The package 3 is formed of a resin which is transparent relative to the light emitted from the light emitting layer 21c. As shown in FIG. 3, the package 3 comprises a rectangular main body 31 and a convex lens portion 6 formed at one side surface of the main body 31. Though not illustrated in the figure, the package 3 is covered with a light shielding film except for the lens portion 6. The light emitted from the light emitting layer 21c is directed to the outside of the package 3 through the lens portion 6.
Referring to FIG. 4, a flat boundary surface 5 can be hypothetically defined between the package body 31 and the lens portion 6. In the prior art LED light source 101, the LED chip is arranged so that one side surface 21c1 of the light emitting layer 21c extends in parallel with the boundary surface 5. Due to such an arrangement, the prior art light source has the following disadvantages.
As described above, when a voltage is applied across the lower electrode 22 and the upper electrode 23, light is emitted from a certain point of the light emitting layer 21c. FIG. 4 illustrates the travel route of light emitted from a light emitting point O located at the center of the light emitting layer 21c. As shown in the figure, the light emitted from the light emitting point O travels in a triangular region having an apex angle (diffusion angle) α. Thereafter, the light is refracted in exiting the light emitting layer 21c to enter the resin package 3. The refractive index of the light emitting layer 21c is larger than that of the resin package 3. Therefore, the light entering the resin package 3 travels in a triangular region having a diffusion angle β which is larger than the angle α. (The diffusion angle α may be 8.4° for example, whereas the diffusion angle β may be 20°, for example.) Then, the light is directed to the outside of the package 3 through the lens portion 6.
With such a structure, only a small portion of the light emitted from the light emitting point is directed to the outside of the package 3. Specifically, when the diffusion angle α is 8.4°, only about 2.3% (=8.4÷360) of the light is directed to the outside of the package 3. Therefore, for irradiating an object with a sufficient amount of light, the power consumption increases or a large LED chip need be used, which is disadvantageous.